Polyhydric alcohol esters of alkyl mercapto fatty acids and oil compositions containing said esters



- are also rust reventives.

United States Patent 3,15%,576 PQLY TYDRHC ALQUHGL ETER 0F ALKYL MER-CAPTQ FATTY AGlDS AND 01L CQMPGSITEQNS CQNTAlNlNG SAM) lid-TEES Harry W.Rudel, Roselle, and William Seitz, Union, NJ assignors to Essa Researchand Engineering Company, a corporation of Delaware No Drawing. FiledJan. 4, 1960, Ser. No.78 4 Claims. (Cl. 25248.6)

This invention relates to polyhydric alcohol esters of alkyl merca-ptofatty acids and to oil compositions containing them. Particularly, theinvention relates to esters which are useful as rust reventives in oilcompositions and are prepared by partially esterifying a polyhydricalcohol withian alkyl thioether of a saturated fatty acid.

In US. Patent 2,884,379, it was disclosed that certain alkyl mercaptofatty acids were oil soluble and showed excellent rust inhibition in anoil vehicle. However, the use of these acids are limited since they arenot particularly suitable, or must be employed in very lowconcentrations, in many applications where acidic additives are notdesirable. Thus, use of these acids, excepting in very lowconcentrations, is not generally desirable in stationary steam turbineoils, marine E.P. turbine oils, gencral purpose industrial oils, certaintypes of hydraulic oils, greases, middle distillate fuels and dyed motorand aviation gasolines. The use of an acidic type of inhibitor may bedetrimental in applications involving high temperature contact withnon-ferrous metals because of their corrosive action. Their use withdyes in gasolines and materials that are color sensitive to acid-basereactions, is also undesirable. Their use in distillate fuels as pipeline rust inhibitors provokes the formation of soluble iron soaps thatsubsequently form induction system deposits in internal combustionengines.

It has now been found that by further reacting alkyl mercapto fattyacids with a polyhydroxy compound to form an alcoholic compound, thattheresulting esters not only retain the excellent rust inhibition of theacids per se, but are superior in that they are neutral in reaction andmay be employed in any desired concentration in lubricants withoutadversely affecting non-ferrous metal corrosion. They may also beemployed in motor fuels without romotin the above inade uacies relativeto color reaction and iron soap formation.

It has been further found that the additives of the invention aresuperior in certain respects, such as emulsion forming tendency, toother polyhydric alcohol esters which This undesirable emulsionformingtendency is surprisingly slight with the mercapto acid esters of theinvention, particularly when compared to fatty acid esters ofpolyhydroxy materials, such as; sorbitan monooleate, pentaerythritoldioleate, glyceryl mono-stearate, polyoxyethylene sorbitan mono-laurateand unsubstituted fatty acid esters of trimethylol propane.

The esters of the invention have the general formula:

wherein R is a straight or branched chain alkyl radical containing 4 to22, preferably-8 to 18 carbon atoms; R is a C to C aliphatic saturatedhydrocarbon radical; while R" contains 2 to 18, preferably 3 to 10carbon atoms and is an aliphatic, saturated hydrocarbon radical or anether-interrupted aliphatic, saturated hydrocarbon radical, whichhydrocarbon radicals may be substituted with 1 to hydroxy groups.

, The esters of the above formula can be prepared by esterifying alkylthioether fatty acids of the general formula:

RSR'COOH wherein R is an alkyl radicalof 4 to 22 carbon atoms 3,l58,575Patented Nov. 24, 1964 and R is a saturated aliphatic hydrocarbonradical of 1 to 4 carbon atoms. Examples of such acids include laurylmercapto acetic acid, C OX0 mercapto acetic acid, hexyl beta mercaptopropionic acid, and Z-ethylhexyl alpha mercapto valeric acid. Methods ofpreparing such acids are described in detail in US. Patent 2,884,379.

The polyhydric alcohols, which may be utilized in forming the desiredesters, include trimethylol propane, pentaerythritol, hexitol, sorbitan,glycerin, etc.

The esterification is carried out by reacting 0.25 to 1.0 moles of thepolyhydric alcohol per mole of the acid, depending upon the hydroxylgroups in the alcohol, under conventional esterification conditions. Ifdesired, 0.1 to 5.0 wt. percent based on the totfl amount of acid andalcohol reactants, of an esterification catalyst can be used. Suitablecatalysts include toluene sulfonic acid, sulfuric acid, hydrogenfluoride, sulfo salicylic acid and sodium acid sulfate. However,generally the reaction will proceed sufficiently fast without acatalyst. Also, it may be desirable to use 25 to 200 wt. percent, basedon the total amount of acid and alcohol reactants, of an inert waterentraining agent such as toluene, xylene, mesitylene, Varsol, kerosene,halogenated solvent such as perchloroethylene, or any other liquidsolvent which is immiscible with water and has the desired boilingtemperature.

The esterification is carried out in a conventional manner by heatingthe reactants and driving off the water. When the stoichiometric amountof water is removed, then the reaction mixture maybe stripped at apressure of about 10 to 760 mm. Hg and a pot temperature of to 400 F. toremove the entraining agent any other volatile materials. The remainingester residue can be used without further purification if made withoutan acid catalyst. If a catalyst has been used, it will usually bedesirable to wash the reaction product with aqueous sodium hydroxide, orsodium carbonate and water, followed by drying over a desiccant such assodium sulfate or anhydrous calcium chloride and filtering prior to thestripping step.

The ester can be dissolved in hydrocarbons, to inhibit rusting, inamounts varying from about 0.03 to 10.0 wt. percent, preferably 0.05 to6.0 wt. percent, based on the total composition. The hydrocarbon may bea mineral oil such as lubricating oils, slushing oils, kerosene, or itmay be a fuel such as motor gasoline, aviation gasoline, jet fuel,furnace oil, or it may be a grease.

Other additive materials may also be added to the hydrocarbon along withthe ester to enhance other desirable characteristics of thecompositions. Such materials as oiliness agents, extreme pressureadditives, thickening agents, pour point depressors, detergents, dyes,and the like which are frequently added to various oil products may beused in conjunction with the ester of the invention to obtain thedesired final composition.

The invention will be understood by reference to the following exampleswhich include a preferred form of the invention.

a EXAMPLE I 289 grams (1 mol) of C 0x0 (tridecyl) mercapto acetic acidhaving a neutralization number of 194, 134 grams (1 mol) of trimethylolpropane and about 500 grams of Xylene were added to a flask equippedwith condenser, stirrer and thermometer; No catalyst was used. Thereaction mixture was heated and maintained at a temperature of about 300F. until 1 mol of water was recovered, which required about 2 hours. Thesolvent was then substantially removed by distillation at a pressure ofabout 50 mm. mercury. The last traces of solvent were removed at 15 mm.pressure and a final pot temperature of 370 F. 395 grams of esterremained as residue. The ester showed the following analysis:

Sulfur8.0%, neutralization number-99 mg. KOH/ gm. ester, andsaponification number-141.8 mg. KOH/ gm. of ester.

parts by weight of the above ester was added to 95 parts by weight of anacid treated naphthenic lubricating oil having a viscosity of :150 SUSat 100 F.

For comparison purposes, a second blend was made up consisting of 5 wt.percent of sorbitan monooleate in the same oil.

A Humidity Cabinet test was run on the above two oil blends as well asthe base oil per se, i.e. without additive. This test was carried in aStandard ]ANH792 Humidity Cabinet. Briefly, this test is conducted bydipping sandblasted steel panels into the oil composition to be testedat room temperature, allowing the panels to drain for two hours, andthen suspending them in the Humidity Cabinet operating at a temperatureof 120 F. and 100% relative humidity. The panels were periodicallyexamined and the test was considered complete when the first threesignificant specks of rust appeared on the panel. In this test, a 5 wt.percent oil blend of sorbitan monooleate is accepted as a standard ofsatisfactory performance.

The results or" this test are summarized in the following table:

Table I HUMIDITY CABINET TESTS Additive: Days Protection 5 wt. percentmercapto acetic acid ester of Example I 5 wt. percent sorbitanmonooleate 10 None 1 EXAMPLE 11 Three blends were prepared in adeasphalted, dewaxed, phenol-treated, mid-continent lubricating oilhaving a viscosity of 165 SUS. at 10 F. These blends were prepared bysimple mixing of the additive into the oil while warming to atemperature of about 70 to 150 F. The blends contained the mercaptoacetic acid ester of Example I, sorbitan monooleate, and a monooleateester of trimethylol propane, respectively, in amounts of 0.1 wt.percent, based on the weight of the oil. These blends were evaluated asrust preventives for steam turbine oils in the presence of bothdistilled water and synthetic sea water. The test was carried out inaccordance with the ASTM D-66546T test procedure. Briefly described, inthis test a standard steel spindle is maintained in contact with arapidly stirred oil composition (300 cc.) and Water cc.) mixture for 24hours at 140 F. At the end of this time the extent of rusting of thepanel is noted.

The blends were also subjected to the Herschel Emulsion test in whichml. of oil and 40 ml. of water are brought to test temperature (180 F.)in a 100 ml. graduated cylinder, agitated with a paddle stirrer at 1500RPM, allowed to stand at the test temperature, and then noting the timeand extent of emulsion breaking. A satisfactory oil will show less than3 m1. of interface emulsion after 30 minutes standing.

The results obtained and the compositions tested are summarized in TableII, which follows:

As seen from the preceding tbale, the ester of the invention was veryeffective as a rust inhibitor and did not have excessive emulsifyingtendencies. On the other hand sorbitan monooleate forms a much morestable emulsion (which is undesirable in many oils, e.g. steam turbineoils) While the trimethylol propane monooleate was a poor rustinhibitor.

What is claimed is:

1. A rust inhibited composition comprising a major amount of liquidmineral hydrocarbon and a rust inhibiting amount of an ester of thegeneral formula:

RSRCOOR"OH wherein R is a C to C alkyl radical, R is a C to C aliphaticsaturated hydrocarbon radical and R is a hydroxy substituted radicalselected from the group consisting of hydroxy substituted aliphaticsaturated hydrocarbon radicals and hydroxy substituted ether interruptedhydrocarbon radicals, said hydroxy substituted hydrocarbon radicalscontaining 1 to 5 hydroxy groups and a total of 2 to 18 carbon atoms.

2. A composition according to claim 1, comprising a major amount ofmineral oil and 0.05 to 6.0 wt. percent of said ester.

3. A composition according to claim 2, wherein R is a C to C alkylradical, R is a C hydrocarbon radical and R" contains 3 to 10 carbonatoms.

4. A mineral oil composition comprising a major amount of a mineral oiland about 0.05 to 6.0 wt. percent of the ester of equimolar amounts of Calkyl mercapto acetic acid and trimethylol propane.

References Cited in the file of this patent UNITED STATES PATENTS2,474,604 \Vasson et a1. June 28, 1949 2,503,401 Mattano et a1 Apr. 11,1950 2,540,093 Brooks Feb. 6, 1951 2,603,653 Kosmin et al July 15, 19522,603,654 Kosmin July 15, 1952 2,884,379 Rudel et a1. Apr. 28, 1959

1. A RUST INHIBITED COMPOSITION COMPRISING A MAJOR AMOUNT OF LIQUID MINERAL HYDROCARBON AND A RUST INHIBITING AMOUNT OF AN ESTER OF THE GENERAL FORMULA: 